The subject matter disclosed herein relates generally to cooling of rotating machines, and more particularly, to rotor cooling.
Electric motors can generate considerable heat, making motor cooling difficult, especially in high power output motors with size and weight constraints. Additionally, in order to avoid excessive wear due to differential thermal expansion, it is important to cool the inner motor components (e.g., rotor) as well as the outer motor components (e.g., casing, stator). Motor cooling can be a challenge for motors that are subjected to a wide range of ambient temperatures, humidity levels, and dust/dirt levels.
A number of different approaches have been implemented to cool electric motors. In one example, the size of the rotor and stator are selected so that heat transfer may occur through use of a gas in the air-gap between the rotor and stator. However, a common disadvantage in this example is increased mass and volume of the machine.
Another method of cooling is to flood the rotor cavity with a dielectric fluid such as oil. As the rotor speed increases, the oil is flung around the machine, resulting in a high heat transfer coefficient along the surfaces of the rotor in contact with the oil. Heat is thus transferred from the rotor to the oil, and then removed from the oil via natural convection, forced convection, or liquid cooling. However, as speed increases, churning losses in the fluid become high and limit the usefulness of this technique.
There is a need to provide an improved rotor assembly cooling system.